According to conventional methods of measuring solution concentration, a test liquid and a reagent liquid are mixed in a predetermined volume ratio and sufficiently stirred until the resultant mixture becomes homogeneous, to prepare a liquid mixture. Then, the liquid mixture is stirred at a predetermined temperature, and upon the lapse of a predetermined period of time, the optical property of the liquid mixture is measured to determine the concentration. In methods of measuring the concentration of a specific component by utilizing biochemical reactions, such as enzyme reactions and antigen-antibody reactions, it is common to set the predetermined temperature to 37° C., which is close to living body temperature. It is also common to set the predetermined period of time to a period of time within which the reaction sufficiently reaches completion. Naturally, since the rate of a reaction depends on temperature, concentration, and the like, a sufficient period of time for the completion of the reaction is set in consideration of the concentration of the test liquid at the predetermined temperature.
As described above, in conventional practice, optical property is measured under conditions where the liquid mixture is sufficiently stirred until homogenized and the reaction would never fail to reach completion. That is, sufficient conditions for homogenization and reaction completion are set.
Also, with conventional apparatuses for measuring solution concentration, a test liquid is retained in a sample cell that is structured to propagate light through the test liquid. This sample cell is in the form of a rectangular parallelepiped, made of, for example, glass, and has transmission faces that are transparent. Thus, light can be propagated through the test liquid. When the test liquid and a reagent liquid are introduced into the sample cell and mixed, the sample cell is detached from the optical system for measuring optical property, and the following operations are performed.
Usually, the top part of this sample cell is open, and a predetermined volume of a test liquid is introduced from the top part using a dropper, a pipette, a syringe, or the like. Subsequently, a predetermined volume of a reagent liquid is mixed thereinto such that the volume ratio of the test liquid to the reagent liquid is constant. Thereafter, the resultant mixture is sufficiently stirred in the sample cell with a stirring stick, stirrer, or the like until it becomes homogenized, and the whole sample cell is kept at a predetermined temperature, for example, in a constant-temperature bath. After the lapse of a predetermined period of time, the sample cell is remounted onto the optical system, and the optical property of the liquid mixture in the sample cell is measured.
However, there have been problems in that conventional solution concentration measuring methods involve a large number of processes and conventional solution concentration measuring apparatuses are large-scaled. Further, there has been another problem of requiring increased measurement time. Therefore, there is a demand for solution concentration measuring apparatuses having a simple structure without a constant-temperature bath and the like, as well as solution concentration measuring methods capable of easy automation.
Further, there has also been another problem in that the processes of loading and unloading the sample cell cause a slight change in the position of the optical system, possibly leading to errors in measurement results. Furthermore, still another problem has been that complicated operations are necessary, and hence, operation mistakes, etc. tend to occur, thereby resulting in poor reliability.
In consideration of the above-mentioned problems, an object of the present invention is to provide a highly reliable method of measuring solution concentration capable of easy automation, as well as a highly reliable, small-sized apparatus of measuring solution concentration capable of easy automation. The present invention further provides a solution concentration measuring method and a solution concentration measuring apparatus which can reduce the time necessary for homogenization and/or reaction completion to the requisite minimum, thereby enabling a reduction in measurement time.